1. Field of the Invention
The present invention relates to inspection technologies for inspecting substrates having fine circuit patterns such as semiconductor products and liquid crystal products, and more particularly to an inspection method and apparatus for inspecting circuit patterns formed by using an electron beam.
2. Description of the Related Art
An inspection apparatus for inspecting semiconductor wafers will be described by way of example. Semiconductor devices are manufactured by repeating a process of transferring a pattern formed on a semiconductor wafer by a lithography process and an etching process. Defective patterns and foreign matters formed by the lithography process and etching process during the semiconductor device manufacture processes influence greatly the manufacture yield of semiconductor devices. It is therefore necessary to detect at an earlier stage or in advance the generation of abnormalities and defects.
A variety type of many defects exist at the leading stage and development stage of manufacture processes using semiconductor wafers. Since the causes of defects are different among the types of defects, different countermeasure methods and positions are used. It is difficult to countermeasure all defects at a time, and there are defects influencing together. It is therefore rare that one countermeasure becomes sufficient. If it can be confirmed that the number of particular defects reduces before and after a plurality of countermeasures, these countermeasures are effective. However, if a variety of many defects exist at the earlier stage, it is very difficult to find which defects among a number of detects are reduced by which countermeasure. Developers of manufacture processes have studied these defects and paid knowledge and labor in finding the optimum conditions of processes, and have relied largely upon the experience of those skilled in the art.
Known apparatuses for inspecting defects on a pattern on a semiconductor wafer include an optical inspecting apparatus which irradiates white light on a semiconductor wafer and compares similar circuit patterns on a plurality of LSIs by using optical images, an SEM type visual inspecting apparatus which detects secondary electrons and reflected electrons generated by irradiating an electron beam to obtain an image which is compared with a reference image, to thereby detect abnormalities such as defects and foreign matters, and other inspecting apparatuses. SEM is an abbreviate term for Scanning Electron Microscopy.
With these inspecting apparatuses, an inspected image is compared with a reference image, only the images having different gradation values obtained by binarizing a luminance are extracted to use them as the abnormal portions. Defect images are formed or the positions of the abnormal portions on the semiconductor wafer are displayed, to thereby display a plurality of defects for an operator. The operator transmits data of a defect distribution displayed as a defect map on the semiconductor wafer to another analyzing apparatus. The analyzing apparatus selects several defects from a plurality of defects and makes a detailed analysis by using an observation image obtained by irradiating an electron beam.
A defect map displays generally many defects having a variety type of defect causes, and the operator wishes to find that an analysis of which defect is most urgent. Practically, this has relied conventionally upon the skill of the operator. Defects extracted and displayed on a defect map indicate only the abnormal portion having a different image. Abnormal portions which are not defects are extracted in some cases, and a distribution of a variety type of defects on a semiconductor wafer is displayed without any discrimination among them.
From this viewpoint, it has been tried to make the inspection apparatus not only merely display a defect map, but also extract the defects unnecessary for a defect analysis and display only necessary defects as defect data. For example, the optical inspecting apparatus cannot detect non-conduction defects and electric short-circuits of a semiconductor device formed on a semiconductor wafer during a contact hole forming process. However, since the SEM visual inspecting apparatus can detect such non-conduction defects and short-circuits, it has been tried to discriminate between the non-conduction defects and the short-circuits from the defect image and the coordinate values of the defect on the semiconductor wafer (for example, refer to JP-A-2002-124555 (Page. 8, FIG. 6).
Although not pertaining to the manufacture processes for a semiconductor device, a method is know which classifies defects in accordance with a plurality of characteristic quantities such as the contour and luminance of each manufacture defect (for example, refer to JP-A-2002-174603 (Page. 3, FIG. 6). However, no specific description has been found which illustrates a method of eliminating unnecessary defects extracted with a SEM visual inspecting apparatus during the manufacture processes of semiconductor devices.